Method of fine grinding of cement material



Patented Apr. 18, 1933 UNETED STATES PATENT OFFICE CARL PONTOPPIDAN, OF I-IOLTE, COPENHAGEN, DENMARK, ASSIGNOR TO F. L. SMIDTI-I & (30., OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY METHOD OF FINE GRINDING OF CEMENT MATERIAL No Drawing. Application filed March 13, 1930, Serial No. 435,653, and in Great Britain March 21, 1929.

In the manufacture of Portland cement it has been found desirable to grind the cement material, such as cement clinker or cement raw material, to a greater degree of fineness than was formerly deemed necessary. In the dry grinding of material with grindlng bodies, such as flint pebbles, 0r Cylpebs,'or the like, there is observed a tendency of the fine particles of the material being ground to adhere to the surface of the grinding bodies, whereby the efficiency of the grinding bodies and of the mills in which the grinding is carried on is considerably reduced. In the effort to overcome this tendency, in the development of the present invention, it has been discovered that the tendency of the fine particles to adhere to the grinding bodies is due in part, at least, to the fact that by reason of the friction between the material and the grinding bodies in the'process of grinding the grinding bodies themselves become charged with static electricity and that there exists a difference of polarity or a difference of electrical potential, or of both, which results in attraction of the fine particles of the material to the grinding bodies and consequent adhesion. It is therefore proposed, the present invention, to prevent or at least to diminish greatly the attraction of the fine particles to the grinding bodies by reason of the relative condition of the material and the grinding bodies and to that end the invention consists, generally speaking, in altering the electrical relation of the material and the grinding bodies as by changing the polarity or the electrical potential of the grinding bodies. Such change in the relative electrical condition may be accomplished by reducing the difference of electrical potential, as by effecting the discharge of the static electricity from the grinding.

It will be observed that the desired change in the electrical relation may be effected in any of various known ways to change the electrical condition of the material or the grinding bodies, as by the introduction of a suit-able electrical charge. It has been found, however, that in the grinding of cement clinker or of cement raw material, in the usual cement grinding mills, with grinding bodies, it is most convenient to add to the material, either before the grinding or during the grinding, a relatively small quantity, varying under different conditions and different materials and substances, from onehalf of one per cent to ten per cent of the weight of the material to be ground. Various substances have been found to yield satisfactory results. A carbonaceous material, such as the pulverized coal commonly used for fuel in the burning of cement raw mate rials in rotary kilns, can be employed advantageously and gives satisfactory results.

To avoid the discoloration of the material which is effected by the addition to the material to be ground of a carbonaceous substance this substance can Wholly or partly be removed after the grinding of the material by heating or chemically acting upon the added substance so as to produce a distillation, burning or oxidation.

I claim as my invention:

1. The improvement in the method of fine grinding of dry cement material with grinding bodies which consists in adding to the material a carbonaceous substance whereby the electrical potential of the grinding bodies is altered and the attraction of the particles of material to the grinding bodies is diminished and the coating of the grinding bodies With such particles is prevented.

2. The improvement in the method of fine grinding of dry cement material with grinding bodies which consists in adding to the material a carbonaceous substance whereby the electrical potential of the grinding bodies is altered and the attraction of the particles of material to the grinding bodies is diminished, and after grinding removing the added carbonaceous substance by chemical reaction.

This specification signed this 24th day of February, A. D. 1930.

CARL PONTOPPIDAN. 

